1. Field of Invention
The invention relates generally to the field of oil and gas production. More specifically, the present invention relates to a perforating system. Yet more specifically, the present invention relates to a perforating gun coupled to a plug.
2. Description of Prior Art
Perforating systems are used for the purpose, among others, of making hydraulic communication passages, called perforations, in wellbores drilled through earth formations so that predetermined zones of the earth formations can be hydraulically connected to the wellbore. Perforations are needed because wellbores are typically completed by coaxially inserting a pipe or casing into the wellbore. The casing is retained in the wellbore by pumping cement into the annular space between the wellbore and the casing. The cemented casing is provided in the wellbore for the specific purpose of hydraulically isolating from each other the various earth formations penetrated by the wellbore.
FIG. 1 illustrates one example of a known operation for cementing a casing within a wellbore. As shown, a vertical wellbore 5 lined with casing 7 is formed through a subterranean formation 9. An annulus 8 exists in the space between the wellbore 5 and casing 7; cement 11 is forced into the annulus 8 to bond the casing 7 within the wellbore 5. This typically involves first injecting cement 11 into the casing 7 and landing a wiper plug 13 in the casing 7 above the cement 11. The wiper plug 13 shown includes a textured outer surface that seals against the casing 7 inner diameter preventing cement 11 flow between the wiper plug 13 and the casing 7.
Completion fluid 15 is pumped from an injection system 17 in the wellbore 5 above the wiper plug 13. Pressure from the fluid 15 forces the wiper plug 13 and cement 11 toward the wellbore 5 bottom. Sufficient applied pressure forces the cement 11 past the end of the casing 7 and to the wellbore 5 bottom. There the cement 11 enters the annulus 8 bottom and flows upward in the annulus 8 forced by the continued inflow of the pressurized completion fluid 15. Ultimately, the wiper plug 13 reaches the wellbore 5 bottom and couples with a float collar (not shown), where the plug 13 will likely remain indefinitely, unless the wellbore 5 depth is later increased. The cement 11 flowed into the annulus 8 is allowed to cure and set before further downhole operations are commenced.